1. Field of the Invention
The present invention relates to an antireflection coating, and also relates to a display device including the antireflection coating.
2. Description of the Related Art
In a display device that uses an electrooptical device such as a liquid crystal or an electroluminescence (EL) device, an antireflection coating having a low reflectance and high light blocking property in a visible light region is generally placed between respective pixels. For example, in a color liquid crystal display panel, an antireflection coating that divides three primary color (i.e. Red, Green and Blue) filter patterns is placed on a transparent substrate such as glass. It is thereby possible to prevent mixture of colors or interference between the adjacent three primary color filter patterns. Further, by blocking light in a display light degradation area at the end of liquid crystal pixels, it is possible to increase the contrast of a display image and achieve a higher quality image. In order to satisfy the above characteristics, the antireflection coating should be such that a highly accurate pattern can be obtained easily and reflection of light at least from a display surface is low.
As such an antireflection coating, a Cr film having a low reflectance or a Cr alloy film predominantly composed of Cr (with a reflectance of about 60% at a wavelength of 550 nm) has been used. Further, a Cr (upper layer)/CrOy (lower layer) laminated film in which a thin film of Cr oxide (CrOy) (y is a positive number; which is the same below) and a Cr film are sequentially laminated and which has low reflection characteristics (with a reflectance of 10% or lower at a wavelength of 550 nm) with use of an optical interference effect in the CrOy thin film has been used. The Cr film or the Cr/CrOy laminated film can be patterned easily and highly accurately by general photolithography and wet etching using a drug solution.
However, if hazardous hexavalent Cr ion is contained in a waste liquid that contains Cr ion generated in the process of wet etching, an increase in cost for the process of processing the hazardous waste is inevitable, and an alternative technique has been desired in terms of environmental issues.
In order to address the above concern, an antireflection coating that does not contain Cr has been proposed. For example, an antireflection coating made of an Fe/FeOy laminated film is proposed in Japanese Unexamined Patent Application Publication No. 09-101404, an antireflection coating made of a Ni—W—Zr/Ni—W—Zr—Oy laminated film is proposed in Japanese Unexamined Patent Application Publication No. 10-333137, and an antireflection coating made of a Ti—Mo—Ni film is proposed in Japanese Unexamined Patent Application Publication No. 2001-311812. Further, an antireflection coating having a laminated structure of a first layer made of oxide, nitride or oxynitride of an alloy of Ni and Ti, Zr, Nb, Ta, Si, W or Mo and a second layer made of an alloy, nitride or carbide of Ni and Ti, Zr, Nb, Ta or Si is proposed in Japanese Unexamined Patent Application Publication No. 11-52126. Furthermore, an example of using a lamination of a low refractive index film and a conductive nitride film having a high heat resistance that is predominantly composed of a metal selected from Ti and/or Zr and further contains at least one kind of metal selected from a group of Al, Mo, Cr, Nb, Hf, Ni, Co, Fe, Pd, Ag, Au and Pt as an antireflection coating is disclosed in International Patent Publication No. WO00/48204.
Further, a structure in which an aluminum nitride film is formed on the surface of an Al alloy line formed on a semiconductor substrate is disclosed as a structure having an antireflection function for light with a wavelength of 200 nm or less, though it is an example of a semiconductor device, in Japanese Unexamined Patent Application Publication No. 10-64909. Further, as another example of a semiconductor device, a structure in which an AlN coating layer made of a stoichiometric Al50N50 film is laminated on Al or Al alloy formed on a semiconductor substrate is disclosed as a structure having an antireflection function, an etching stopper function and an Al or Al alloy protection function in Japanese Unexamined Patent Application Publication No. 09-252001. Furthermore, an example in which a structure composed of a glass base, a bottom antireflection layer, a heat ray reflection layer and a top antireflection layer and using an AlN layer of a substantially stoichiometric composition as the bottom antireflection layer is used as an example of a glass lamination that can be applied to a sunlight control filter is disclosed in Japanese Unexamined Patent Application Publication No. 2000-229379.